Chipseal vs Hotmix

[Sketchy_Racer]

I don't think that's right.

Chip-seal has a greater resistance to skidding in the wet because it has a higher level of grip than hotmix. Even the road-code acknowledges this:

http://www.ltsa.govt.nz/roadcode/abo...d-surface.html

You believe them?

The definition of grip is the amount of friction one can make between two objects. chip seal with its high points and valleys create an illusion of more grip because "its a rough surface" therefore should create more friction. In some ways true, but it also has a lot lower surface area for the tyres to contact on, meaning less available friction between the two.

Why do you think racing tyres are bald or "slick" .. It's to create the maximum amount of area for the tyre to create friction with track. The grooves in your tyres actually reduce the available grip in dry conditions, at a compromise that it helps with water dispersion in the wet.

Hotmix has a much smoother surface giving a much larger area for your tyres to make contact with, therefore creating more grip.

What oil residues on those surfaces change things altogether but for this argument, lets say they are perfectly clean.

[Forest]

You believe them?

The definition of grip is the amount of friction one can make between two objects. chip seal with its high points and valleys create an illusion of more grip because "its a rough surface" therefore should create more friction. In some ways true, but it also has a lot lower surface area for the tyres to contact on, meaning less available friction between the two.

I'm more than happy to agree that hotmix has superior grip in dry conditions.

However I'm inclined to believe that chip-seal has superior grip in the wet.

[Sketchy_Racer]

I'm more than happy to agree that hotmix has superior grip in dry conditions.

However I'm inclined to believe that chip-seal has superior grip in the wet.

Fair enough, what makes you believe that?

I did used to think the same, until I realised what made me think that Chip seal had more grip was a mental thing (I thought it did, therefore I felt that it did when I was riding) Until I thought about it in more 'scientific' way and the funny thing is now with more riding experience and getting to feel how a bike reacts when pushed hard on different surfaces I feel that asphalt has a much higher grip level in the wet.

[Pussy]

I'm more than happy to agree that hotmix has superior grip in dry conditions.

However I'm inclined to believe that chip-seal has superior grip in the wet.

If you're happy to believe that, all is good!
I, however, would much rather ride on hotmix in the dry AND the wet, and much prefer the better grip on hotmix in the wet

[Big Dave]

Whatever perfect world you care to therorise in, and the conclusions you draw, it bears little resemblance to the imperfect condition of the seal on NZ's roads.

I would prefer hotmix in any conditions. real world consistency of the surface/grip being the key.

Then there is tyre wear.

[Big Dave]

A minister in the former government told me that they could fix the road surface in NZ - but it would be expensive.

He wanted 'someone' to research what the human and medical cost of the current chip sealed state was - and compare it to the cost of actually fixing the piles of loose crap and the shiny black death.

I kinda glazed over at the enormity of the task and now the govt has changed.

[Forest]

It's fairly well known that the coarse chip-seal used in the South Island wears down bike tyres quicker than other road surfaces.

Doesn't that meant that chip-seal has better grip?

I found some information which relates to the size of the chip in the chip-seal.

21. Is a road with big chip safer than a smoother road?

No, not at all. What makes a road safe is how much grip (skid resistance) vehicle tyres have on the road. This is a combination of how big the chips are in terms of whether they stick out of the bitumen, and how the surface of the chip looks.

Some of the chips are very, very small, like the relatively soft volcanic andacites. But even though the chip is small it has a high skid resistance. Transit keeps monitoring skid resistance and uses the standards that are used in the United Kingdom. There's no simple rule that 'big chips give you better grip'.

What does matter is the way the road is built. If you keep building a road out of big chips on top of big chips on top of big chips, layer after layer, every 10 to 12 years, then eventually you will probably get a pudding of black bitumen with big stones in it.

From here

[SpeedMonger]

I can give you some details on this being a "roading person".

This is actually a fairly complex issue.

But to clear up some definitions;

Tar - "tar" a derivitive of coal has not been used on NZ roads for decades.

Bitumen - Bitumen is what is left from crude oil once all of the useful things have been extracted from it such as fuels and light oils. It come in different grades for different applications. They an be modified with polymers and other additives to improve performance.

Sealing Chip - is a crushed aggregate product (98% minimum) that comes in six different grades or sizes (specified by Transit NZ). The aggregate used must meet several durability criteria including resistance to polishing "PSV" which relates to skid resistance on the road.

Asphalt - Also known as Hotmix, is a blend of various sized aggregates and bitumen put through a specialised blending / heating plant. There are different varieties for different purposes ranging from wearing, structural and water dispersing etc.

Skid resistance is measured by spraying water on the road in front of a wheel that has a force applied to the point of skidding, the more force = more skid reistance.

Chip Seal Pavements

A chip seal pavement is constructed by spraying bitumen over the new pavement or existing seal and spreading sealing chipover the top, which is then rolled to embed the chip into the bitumen. It is critical to get the right application rate for the size of chip to be used, too much and you geed bleeding or too little and chip loss can occur. There are many types of seals for different purposes. Firstcoats on new roads use large chip, and subsequent reseals generally use smaller chips that fill in the gaps between the larger stones. The PSV of the aggregate dictates what scenario the aggregate can be used in, ie a high speed corner requires a higher PSV than a straight section of the same road. The PSV is dependant on the microtexture fn the stones themselves. An aggregate that polishes with traffiking will have low microtexture and lower skid resistance. High PSV aggregates have rougher surfaces and larger grain sizes that abrade with traffiking giving consistent high skid resistance over time but are less durable.

Chipseals have high macrotexture (gaps between the stones), this means it can disperse water easily and therefore should have better wet weather grip than a asphalt made from the same aggregate.

The bitumen used is generally cutback with diluents to make it easier to spray and for ductility under various weather conditions. they also have adhesion agents added to help make the stones stick. Different additives are required depending on the aggregate's chemistry makeup. When a bitumen is used that is diluted too far for a given climate, it's softening point will be too low meaning it soften to the point where stones can be plucked out - this is called "flushing", you then just get left with the black slippery bitumen. If the bitumen does not adhere to the stones because they are dirty or incompatible you also get flushing.

Asphalt

Asphalts fall into two types, open graded and dense graded. Dense graded mixes generally have relatively low surface texture (macrotexture) as they are designed to compact well and interlock for strength and durability. Open grade mixes are designed to drain surface water and are laid over the top of a dense mix. They have high macrotexture but little microtexture, so they have improved wet skid resistance but potentially less dry skid resistance.

Asphalt is more expensive to produce and is logistically more difficult to deliver and apply as it has strict temperature control requirements and requires specialised plant.

So to summarise, in the dry there is no real difference between the two types, an asphalt should be better because of the increased contact patch to microtexture but when water is added then the surface with the best combination of macrotexture and microtexture should win ie a high PSV chip seal - as the water acts as a barrier between the rubber and the stone microtexture on a dense asphalt.

Still awake?? lol.

[Big Dave]

Flushing. Apt name for that crap!

[Forest]

So to summarise, in the dry there is no real difference between the two types, an asphalt should be better because of the increased contact patch to microtexture but when water is added then the surface with the best combination of macrotexture and microtexture should win ie a high PSV chip seal - as the water acts as a barrier between the rubber and the stone microtexture on a dense asphalt.

Still awake?? lol.

Thanks - I was fairly certain that was the case.

It appears that chip-seal really does offer better grip in wet conditions.

[Bass]

I'm with Forest here.
We all know that the "shiny patches" (excess bitumen) have almost no adhesion in the wet. Asphalt, hot mix, whatever, of necessity has all the stone coated with bitumen.
The grip (resistance to sliding) is proportional to the perpendicular contact force and the coefficient of friction.
The "shiny patch" syndrome says to me that the coefficient of friction is higher between tyre and wet stone than it is between tyre and wet bitumen.

In the dry, I suspect that surface condition is more important than surface content.

[Okey Dokey]

I cannot compete with all this technical talk. I will repeat, however, that I certainly found better grip on chip & tar roads in the wet than on hotmix. In a light drizzle the hotmix was okay, but a soon as it rained it was as if the entire road was covered in standing water. It was perfect for aquaplaning and not very nice to ride on. In the "real world" I would much rather be on the chip type surface.

I also agree with the poster who mentioned the amount of crashing that occurs in bike races on hotmix when it rains. I'm sure that if these top guys experience loss of traction, than we humble mortals should take note.

I also suspect that hotmix is used here on roundabouts not because it provides superior grip, but because it copes better with the pressures of heavy vehicles turning.

[MSTRS:Me]

... lighter coloured material (I think it is greywacke from the South Island) to prevent it from heating up during summer. That's why it has a different colour to the rest of the Auckland motorway system.
...

I would hope that greywacke is not used. It is known colloquially as Rotten Rock. There is a good reason for that. It is a particular type of sedimentary stone, that was formed in layers that have a high clay content (I think). It is as hard as hell UNTIL it is exposed to the elements. Then it quickly breaks down and becomes very crumbly. Not at all suitable for roading chip.

[racerhead]

Ok Ive been reading over the last few pages and from what I have seen one of the big benefits of hotmix is its consistency. Example, with hotmix the surface is very uniform in its grip levels in either the wet or dry but with the chipseal the surface grip can change rapidly due to a varying amount of chips/bitumen. So IMO hotmix wins in the dry and hotmix wins in the wet even though it has less grip than chipseal but it does have consistency which will give you the confidence to corner at or near the limits of grip.
Example: Taking a wet corner on hotmix will be easier to hold a bike on its grip limit while with chipseal you can have the bike on its grip limit but you hit a patch with less chips and less grip so you get a slide which will mess with your head.

[Big Dave]

Thanks - I was fairly certain that was the case.

It appears that chip-seal really does offer better grip in wet conditions.

Then there is the reality, flushed with adhesion.
The last time I rode hwy 4 - 20% of the surface was gone in long sections.